ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
Scanning tunneling microscopy (STM) studies of 1 μm thick films of single crystalline Fe3O4 grown on MgO(001) indicate that repeated annealing of the sample in UHV causes Mg diffusion through the Fe3O4 film. The onset of this effect was clearly seen by STM at room temperature for samples raised above 400–430 °C. It appears that the annealing process causes the migration of Mg from the substrate entirely through the Fe3O4 lattice, and that the migration tends to fill the surface layer first, with lower layers filling as anneal time is increased. Upon detection of this effect, several complementary sample analysis techniques were employed to determine the extent of the changes observed. X-ray diffraction studies indicate shifts in the lattice constant from the cubic constant of magnetite, Fe3O4, (8.396 Å), which is already strained in thin-film growth on a substrate, further toward the cubic lattice constant of magnesioferrite, MgFe2O4, (8.375 Å) in order to accommodate the Mg that has migrated to the surface. Superconducting quantum interference device magnetometry studies reveal a significant change in the magnetic behavior of the film and large decreases in the saturation moment, remanence, and coercive field. The Verwey transition is greatly altered in these films after the annealing sequence. X-ray photoelectron spectroscopy studies of the films confirm the presence of magnesium in the uppermost layers of the film, and indicate a concentration gradient, with the highest concentrations of magnesium in the surface layer. X-ray fluorescence in scanning electron microscopy qualitatively indicate the presence of magnesium throughout the film, consistent with migration of the magnesium from the substrate. These results are compared with those on an unannealed Fe3O4 film of the same thickness and growth parameters, which shows no magnesium migration into the film during growth up to substrate temperatures of 300 °C. ©1997 American Institute of Physics.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.365161
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